Extruded foamed fibers



Jan. 2s, 1969 E. o. QHSOL 3,424,645

EXTRUDED FOAMED FIBERS OriginalFiled April 30, 1963 55k/zunge I NVENT OR5w/7T 0 05ML ATTORNEYS' United States Patent Otice 3,424,645 PatentedJan. 28, 1969 3,424,645 EXTRUDED FOAMED FIBERS Ernest O. Ohsol,Wilmington, Del., assignor to Haveg Industries, Inc., Wilmington, Del.,a corporation of Delaware Grigiual application Apr. 30, 1963, Ser. No.276,708, now Patent No. 3,275,720, dated Sept. 27, 1966. Divided andthis application July 30, 1964, Ser. No. 392,368 U.S. Cl. 161-175 9Claims Int. Cl. D01f 04; D01f 02 ABSTRACT OF THE DISCLOSURE A drawnlongitudinally oriented liber of a thermoplastic resin foam is providedwith a warm feel and insulating values equivalent to natural fibers, afoam resin core having elongated luminae and an impervious outer skinintegrally united to said core, said core comprising 50 to 95% of thediameter of said liber, said liber having a density between 14 and 45lbs./ cu. ft., said resin being selected from the group consisting ofstyrene polymers, polyethylene, polypropylene, ethylene-propylenecopolymer, polychlorotrifluoroethylene, polymethyl methacrylate, vinylchloride polymers and polyurethanes and the drawing being to an extentof at least 2 times whereby there are highly longitudinally oriented,elongated luminae in the foamed core.

This application is a division of my copending application, Ser. No.276,708, tiled Apr. 30, 1963, now Patent 3,275,720.

The present invention relates to extruded foamed fibers.

When an attempt is made to prepare fibers from low density foams, eLg.,polystyrene foam of a density of 5 lbs/cu. ft., unsatisfactory productsare obtained because the foam does not have sufficient strength to bedrawn.

Problems are also attendant upon the foaming of higher density foams incontrolling the bubble size.

It is an object of the present invention to prepare novel extrudedfoamed iibers.

Another object is lto prepare synthetic fibers having the warm feel andinsulating values of natural fibers such as cotton.

A further object is to develop a novel process for preparing extrudedfoamed fibers.

Still further objects and the entire scope of applicability of thepresent invention will become apparent from the detailed descriptiongiven hereinafter; it should be understood, however, that the detailed`description and specific examples, while indicating preferredembodiments of the invention, are given by way of illustration only,since various changes and modifications within the spirit and scope ofthe invention will become apparent to those skilled in the art from thisdetailed description.

It has now been found that Ithese objects can be attained by extruoingliber of a foamed plastic having a density between 14 (or more desirably18) and 45 lbs/cu. ft., preferably between 20 and 35 lbs/cu. ft., anddrawing the fiber longitudinally to form a rather highly longitudinallyoriented fiber having elongated lumina therein. For best results, it hasbeen found that the foaming should be done in the presence of anucleating agent in order to control the texture of the foam and givenice uniform bubbles. The surface of the liber should be cooled rapidlyprior to or simultaneously with the foaming so that there is acontinuous, integral, non-porous skin on the fiber. The foamed core isat least 50% and normally from 60 to 95 of the diameter of the fiber andpreferably at least of the ber diameter. The balance of the fiberdiameter is the non-porous skin.

The fibers prepared according to the invention have an excellentinsulating value and warm feel. They also have an advantageously highstrength to weight ratio and a relatively low specific gravity comparedto unfoamed fibers. They have superior moisture resistance and chemicalresistance than natural iibers such as cotton, for example.

The skin, coupled with the use of relatively high density foams,supplies the extra strength necessary to draw the fiber.

The fibers are normally foamed as they come out of the extruder throughthe spinneret. Also, they are preferably drawn at this time. The drawingcan be accomplished in either one or a plurality of steps. Also, theextruded fibers can be cooled, wound on rolls and subsequently reheatedand drawn.

The amount of stretching can be from 2:1 up to 20:1 (i.e., from 200% to2.000% Thus, there can be a longitudinal stretch of from .2:1 to 110:1,preferably between 2.5 :l and 5:1 in a first stretching step and astretch of from 2:1 to 10:1 preferably, 2.5 :l and 5:1, in a secondstretching step. Without the external skin it is not possible tosatisfactorily stretch foamed plastic fibers because they will haveinsuicieiit strength at the stretching temperatures. Usually, stretchingis carried out at a little below extrusion temperature. The preferredmode of operation is to stretch substantially immediately afterextrusion so that the core of the ber is warm enough to foam while theskin is cool enough to maintain the form stability of the liber.

To avoid the problem of elastic memory, the drawing is normally donewarm. Thus, for the preparing of foamed fibers used in clothingstretching should be carried out about 250 F., e.g., between 250 F. and350 F. to prevent shrinkage in laundering. Of course, when it is desiredto obtain a crimped wool-like effect, drawing is done at the lowesttemperature commensurate with reasonable drawing speeds. Thus, a drawingtemperature of 26S-290 F. can be employed.

The foamable or foaming plastic comes out of the extruder at 5 Ito 50 or100 feet/min. and drawing is accomplished, for example, by passing thefibers over two rolls rotating at different speeds.

The present invention is useful in forming foamed fibers having anintegral, continuous, external skin from foamed polystyrene, foamedpolyethylene of high density, eg., 0.960, medium density, eg., 0.935, orlow density, e.g., 0.914, foamed polypropylene, foamed copolymer ofethylene and propylene, eg., a 50:50 molar copolymer, foamed vinylchloride polymer, eg., polyvinyl chloride or vinyl chloride-vinylacetate (87: 13) copolymer or foamed polyurethanes. Examples of foamedpolyurethanes are foams made by foaming prepolymers of polypropyleneglycol 2025 molecular weight-toluene 2,4-diisocya11ate,trimethylolpropane-propylene oxide adduct molecular Weight 418- toluene2,4-diisocyanate, 1,4-butanediol-adipic acid polyester-toluene2,4-diisocyanate, glycerine-propylene oxide adduct molecular weight1000-toluene 2,4,6-triisocyanate.

In fact, any of the conventional polyols and organic polyisocyanates canbe used to form the prepolymer to form the foamed polyurethanes. Thus,there can be used any of the polyols, polyisocyanates or prepolymersdisclosed in Knox Patent 3,079,641'or Friedman Patent 3,081,331 inmaking the polyurethanes. The entire disclosure of the Knox andFriendman patents is herein incorporated by reference.

The Vadvantage of incorporating a phosphorus-containing polyol as one ofthe reactants in forming the polyurethane prepolymer is that increasedflame and fire resistance is imparted to the foamed fiber. Thus, therecan be used a prepolymer prepared by reacting toluene diisocyanate witha mixture of 80% polypropylene glycol molecular weight 2025 and 20% tris(dipropylene glycol) phosphite or by using a prepolymer made fromtoluene diisocyanate and a mixture of 75% polypropylene glycol 2025 and25% bis (dipropylene glycol) hydroxypropoxypropane phosphonate.

When employing polystyrene, there can be used normal crystal gradepolystyrene or high impact polystyrene or a mixture containing to 95%normal crystal grade polystyrene and the balance high impactpolystyrene. When employing a thermoplastic styrene polymer, it normallycontains greater than 50% by weight of styrene and preferably at least70% by weight of styrene in its structure, e.g., a copolymer of 70%styrene and 30% acrylonitrile. High impact polystyrenes are frequentlyprepared by polymerizing monomeric styrene in the presence of 21/2% toby weight of a rubbery diene polymer or by polymerizing styrene in thepresence of such amounts of a difunctional material. Examples of highimpact styrene polymers include a terpolymer of 5% acrylonitrile, 5%butadiene and 90% styrene; a copolymer of 5% butadiene and 95 styrene;the product made by polymerizing 95 of styrene in the presence of 5%polybutadiene; a copolymer of 5% chlorosulfonated polystyrene and 2.5%polybutadiene; a blend of 95 polystyrene and 5% of hydrogenatedpolybutadiene containing 35.4% residual unsaturation, polystyrene formedin the presence of 5% hydrogenated polybutadiene containing 4.5% ofresidual unsaturation; a blend of 95 polystyrene and 5% polyisoprene;and a copolymer of 99.5% styrene and 0.5% divinyl benzene.

There can also be used polymerized methyl methacrylate,polychlorotrifluoroethylene, etc.

The invention will be best understood in connection with the drawingswherein:

FIGURE 1 is a schematic illustration, partially in section, showing apreferred overall process; and

FIGURE 2 is a sectional view of the foamed fiber.

Unless otherwise indicated, all parts and percentages are by weight.

EXAMPLE 1 Referring more specifically to the drawings there is provideda Banbury mixer 2. Also, there is provided a polystyrene compositionmade by mixing 50 parts of pellets of high impact polystyrene (FosterGrants Tuflex 216, polystyrene modified with 5% polybutadiene) and 50parts of pellets of regular crystal polystyrene (Koppers Dylene 8). Thiscomposition is designated hereinafter as Composition A.

90 parts of Composition A were mixed for 5 to 10 minutes in mixer 2 with10 parts of Dow-Pelispan 101 (expansible polystyrene beads containing 6%pentane) and 0.5 part of Bayol 35 (a petroleum aliphatic hydrocarbonwhite oil). The mixing was carried out at room temperature. There werethen added as a nucleating agent 0.75 part of powdered sodiumbicarbonate and 0.6 part of powdered anhydrous citric acid and themixture further tumbled for an additional to 20 minutes. The resultingmixture 4 was then added to the extruder indicated generally at 6. Theextruder includes a conventional barrel having a rotatably positionedextrusion screw therein (the barrel and screw are not shown). Thepolystyrene composition is heated to about 325 F. and is under apressure of 2500 p.s.i. in the barrel. The screw forces the compositionalong and it is delivered at a metered rate to the spinning head 8 ofthe extruder. The composition is then forced through the plurality ofspinnerets 10 in the die portion of the spinning head to form fibers 12.The composition is maintained at 300 F. as it emerges through thespinnerets. As the fibers emerge from the spinnerets at a rate of 30ft./min. they are surface cooled 'with the aid of fans 14. These fansare disposed to insure that the outer surfaces of all the fibers arecooled. (In place of air the fibers can be cooled with water, anairwater mixture, nitrogen, argon, etc.) Thus, the fans impart to thefibers a blast of air at above room temperature, eg., at 200 F and at5-100 ft./min. and in the specific example being described the rate ofair flow was at 25 ft./min. The outer surface of the fibers is thuscooled to below the foaming temperature, eg., to 220 F. to form skin 16,as shown in FIGURE 2, while the inner core of the fibers is maintainedabove the foaming temperature, eg., it is kept at 280 F. to form afoamed core 18. The skin formed is continuous and impervious and isintegral with the foam. To be sure that there is no inadvertent foamingof the skin to produce pores the skin is cooled to at least 5 F. belo-wthe foaming temperature of the plastic. The skin, however, should not becooled to such an extent that it is brittle in the stretching operationand, hence, the temperature of the skin should be kept above thetransition temperature of the plastic, e.g., polystyrene, being foamed.

In the specific example the threads or fibers 12 as they issued from thespinnerets were 30 mils in diameter and foamed up to 40 mils diameterdue to the three dimensional expansion of the fibers. The thickness ofthe skin was 4 mils (10% of the diameter of the fiber) and the diameterof the core was 32 mils (80% of the diameter of the fiber). (Thediameter of the fiber is the diameter of the core plus twice thethickness of the skin.) The foam had a density of 30 lbs./ cu. ft.

The fibers 12 then pass between rolls 20 and 22 which serve primarily tochange the direction of the fibers and then pass between draw rolls 24and 26 rotating at a speed such that the draw rate is 150 ft./min.(i.e., to give a 5:1 longitudinal stretch). The diameter of the fibersgoes down to 22 mils in this stretching step. The temperature of the bercore during this stretching is about 280 F. The stretched fibers canthen be wound on a reel or they can be given a second stretch. Thus, thestretched liber 12, which has been cooled to some extent by this time,is introduced into a warming bath 28 of glycerine at 266 F. in which aremaintained direction changing pulleys 30 and 32. The fiber was in thebath long enough for both the skin and core to come to the bathtemperature. After emerging from the bath the liber 12 passes overpulley 34 and is further stretched 4:1 with the aid of a godet wheel(not shown) to produce a final ber having a diameter of 16 mils and adensity of 35 lbs./cu. ft.

The warming bath 28 can alternatively contain any other liquid inert tothe thread composition. Thus, it can be an alloy such as Woods metal.Also, instead of a hot liquid bath, the thread can be reheated for thesecond stretching by using a hot air oven. (By using an alloy, e.g.,Woods metal, for the bath 28 the fiber can be warmed to 290 F. prior tothe second stretching, eg., at 4:1.)

The size of the bubbles in the foamed core is quite small, and theygenerally are less than 2 mils diameter, e.g., 0.01 to 0.5 mil prior tothe initial stretching. As stated, the stretching highly Orients thefibers longitudinally, and the elongated luminae in the foamed core aresimilarly oriented. The skin is oriented but maintains its continuous,impervious condition. The skin has a density of about lbs/cu. ft. andapproximates the density of the unfoamed, polystyrene.

EXAMPLE 2 In another example, using the apparatus of FIGURE 1, there wasemployed as the foamable composition a mixture of 100 parts ofComposition A, 1 part of Celite (diatoma v ceous earth) having absorbedtherein 1 part of pentane (i.e., 2 parts total of Celite-pentane), 0.5part Bayol 35 and a nucleatng agent composed of 0.6 part anhydrouscitric acid and 0.75 part of powdered sodium bicarbonate.

The extrusion temperature was 300 F., the fibers had a diameter of 25mils as they were spun prior to expansion, and the extruded foamedfibers had a density of 25 lbs/cu. ft., and a diameter of 38 mils, andthe core 18 had a diameter of 85% the total diameter of the fibers,i.e., the skin had a thickness of 5.7 mils. The fibers were stretched3:1 in the first step, while the core was at a temperature of 275 F. andthe skin was at a temperature of '215 F. In the second step, theglycerine bath was kept at 285 F. and the second stretching was also ata 3:1 ratio.

The invention is particularly adapted to the extrusion of fibers orfilaments having a diameter of to 100 mils, or even up to 500 mils. Ifthe fibers have a diameter of under 5 mils, then it is not possible toobtain a sufciently thick skin to give strength while also having anysignificant diameter in the expanded core. The fibers, as they arefoamed, expand in volume about 1.3 to 3.7 times and in diameter from 1.1to 1.4 times.

In either Example 1 or Example 2 the final drawn fibers can be heated at275 F. for 1/2 hour to put a partial crimp into them.

The temperature of extrusion and stretching is dependent upon thepolymer of which the foamed fiber is made. The same extrusion andstretching temperatures can be used as with unfoamed fibers of thematerial with the precaution that the skin be formed by surface coolingof the fiber before expansion takes place.

With low density polyethylene, e.g., density of 0.915- 0920, theextrusion is carried out conveniently at 300 to 350 F. at the dieorifice where the threads are formed and stretching is carried out attemperatures of 180 to 210 F. Thus, with a polyethylene of density0.916, molecular weight 20,000, fibers were drawn mils in diameter at atemperature of 320 F. and foamed to a diameter of 28 mils (the foamedcore being 21 mils). The fibers having a foamed core and unfoamed,impervious, integral skin were stretched 4 times in a single stretchingoperation while the skin temperature was at 200 F. Slightly higherextrusion and stretching temperatures are employed with high densitypolyethylene, e.g., density 0.96.

Utilizing polypropylene the extrusion temperature is about 370 to 400 F.and the stretching temperature 260 to 300 F. Thus, using polypropylenemelt index 0.8, it was extruded and foamed at 385 F. and the resultingfibers having a foamed core and a continuous, impervious, integral skinwere stretched 3.5 in a single stretching step at a skin temperature of281 F.

Utilizing polyvinyl chloride and polyurethanes the extrusion temperatureand stretching temperatures are the same as for polystyrene.

It has been found that for best results in foaming the plastic materialit should be mixed with a minor amount of an absorbent having absorbedthereon a volatile liquid which is non-reactive with and which has notmore than a slight solvent action on the polymer. The volatile liquidshould volatilize below the softening point of the polymer.

As the absorbent there can be employed any conventional absorbent infinely divided form, such as diatomaceous earth (Celite), fullers earth,silica gel, e.g., Cab-O-Sil and Hi-Sil, activated alumina, molecularsieves, attapulgus clay and activated carbon. The absorbent is usuallyused in an amount of 0.1-15%, preferably 0.5 to 10% by weight of thepolymer. The absonbent is an inert filler of large surface area butsmall particle size, e.g., 200 mesh or below.

As the volatile liquid there can be used aliphatic hydrocarbons boilingbetween 10 and 100 C., and preferably, between 30 and 90 C., e.g.,petroleum ether (containing primarily pentane or hexane or a mixture ofthese hydrocarbons), pentane, hexane, isopentane, heptane, cyclohexane,cyclopentane, pentadiene and neopentane. Other volatile liquids includemethanol, ethanol, methyl acetate, ethyl acetate, butane, acetone,methyl formate, ethyl formate, dichloroethylene, perchloroethylene,dichlorotetrafiuoroethane, isopropyl chloride, propionaldehyde,diisopropyl ether, dichlorodiffuoromethane, a mixture of pentane with 5to 30% of methylene chloride or other volatile lower halogenatedhydrocarbon.

The amount of volatile liquid absorbed on the absorbent can vary from 5to 150% or more, based on the weight of the absorbent. The amount ofliquid absorbed will depend upon the capacity of the absorbent for theparticular liquid. Normally, the absorbent containing the volatileliquid will appear to be a dry powder. The volatile liquid employedshould be one which is non-reactive with the particular polymeremployed. Usually, the amount of volatile liquid will be 0.1 to 15% byweight of the polymer, e.g., polystyrene, to be expanded. The amount ofvolatile liquid will depend upon the extent of foaming desired. Ingeneral, the greater the amount of absorbed volatile liquid in thepolymer-absorbent mixture the more the expansion. It has -been foundthat good expansion can be obtained using very small amounts of thevolatile liquid.

It is also very desirable to include a nucleatng agent to control theuniformity and size of the bubbles in the closed cell foam. The celldiameter normally is not over 2 mm. and, preferably, is from 0:01 to 0.5mm. (before stretching).

When a nucleatng agent is employed, it is used in an amount of from 0.02to 10% of the total polystyrene by weight. Preferably, 0.4 to 2% of thenucleatng agent is used.

Conventionally, the nucleatng agents are made up of two materials whichreact to form carbon dioxide and water. The two materials are normallyused in approximately equivalent amounts. As the carbon dioxideliberating materials there can be used ammonium, alkali and alkalineearth carbonates or bicarbonates, e.g., ammonium bicarbonte, sodiumbicarbonate, sodium carbonate, potassium bicarbonate, calcium canbonate.The other material is an acid or acid-reacting salt, preferably solid,which is sufficiently strong to liberate the carbon dioxide from thecarbonate or bicarbonate. Generally, the acid has at least 3.0milliequivalents of acidic hydrogen, and preferably at least 10.0milliequivalents, per gram. The acid can be organic or inorganic.Suitable acidic materials include boric acid, sodium dihydrogenphosphate, fumarie acid, malonic acid, oxalic acid, citric acid,tartaric acid, potassium acid tartrate, chloroacetic acid, maleic acid,succinic acid and phthalic acid. In place of the anhydrous acids orsalts there can be used the solid hydrates, e.g., oxalic acid dihydrateand citric acid monohydrate.

While not essential, there can also be added a wetting agent, such asBayol 35 (a petroleum aliphatic hydrocarbon white oil), kerosene havingan average of at least 8 carbon atoms in the molecule,alkylphenoalkylene oxide adducts, e.g., Triton X- (toctylphenolethyleneoxide adduct having 10 ethylene oxide units in the molecule), sodiumlauryl sulfate and sodium dodecylbenzene sulfonate. The wetting agentcan be nonionic or anionic.

The foamed fibers have excellent insulating qualities, a warm feel, highstrength to weight ratio and a low specific gravity. They can be used inplace of cotton and have superior moisture resistance and chemicalresistance to cotton. They can be employed in making clothing, seatcushions and wherever plastic fibers or natural fibers, such as cottonand wool, are employed.

What is claimed is:

1. A drawn longitudinally oriented ber of a thermoplastic resin foam,said ber -consisting of (1) a foam resin core having elongated luminaeand (2) an impervious outer skin integrally united to said core, saidcore comprising 50 to 95% of the diameter of said fiber, said fiberhaving a density between 14 and 15 lbs./ cu. ft., said resin beingselected from the group consisting of styrene polymers, polyethylene,polypropylene, ethylene-propylene copolymer, polychlorotriuoroethylene,polymethyl methacrylate, vinyl chloride, polymers and polyurethanes andthe drawing being to an extent of at least 2 times whereby there arehighly longitudinally oriented, elongated luminae in the foarned core.

2. A fiber according to claim 1 whren the core is 60 to 80% of thediameter of the ber, the ber has a density between 20 and 35 lbs./ cu.ft. and has a diameter between and 500 mils prior to drawing.

3. A ber according to claim 1 wherein the fiber is made of polyethylene.

4. A ber according to claim 1 wherein the ber is made of polypropylene.

5. A ber according to claim 1 wherein the fiber is made ofethylene-propyIene copolymer.

6. A fiber according to claim 1 wherein the fiber is made ofpolyurethane.

7. A fiber according to claim 1 wherein the fiber is made of a vinylchloride polymer.

8. A fiber according to claim 1 wherein the fiber is made of a styrenepolymer.

8 9. A ber according to claim 8 wherein the core is 60 to 80% of thediameter of the ber, the fiber having a density between and 35 1bs./cu.ft. and having a diameter between 10 and 500 mils prior to drawing.

References Cited UNITED STATES PATENTS 2,492,425 12/ 1949 Hall et al.264-54 2,893,877 7/ 1959 Nickolls 264--48 X 3,059,251 10/1962 Pollock161-175 2,948,048 8/1960 Jankens 161-178 3,227,664 1/1966 Blades et al161-178 3,069,406 12/ 1962 Newman et a1. 161-172 FOREIGN PATENTS 854,58611/1960 Great Britain.

OTHER REFERENCES Fibre Structure, Hearle and Peters, Butterworth and 20Co., Ltd., 1963, p. 149, lines 9 et seq. and p. 159, middle paragraph.

Teach, William C., and George C. Kiessling, Polystyrene, ReinholdPublishing Corporation, New York, 1960, pP. 123-124.

ROBERT F. BURNETT, Primary Examiner.

I. D. FOSTER, Assistant Examiner.

U.S. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 ,424,645 January 28 1969 I Ernest O. Ohsol It is certified that errorappears in the above identified patent and that said Letters Patent arehereby corrected as shown below:

Column 7 line 7 "l5" should read 45 Signed and sealed this 17th day ofMarch 1970 (SEAL) Attest:

Edward M. Fletcher, Jr. SCHUYLER,

Attesting Officer Commissioner of Patents

